1. Field of the Invention
The present invention relates to a puller driving structure, and more particularly to a puller driving structure capable of preventing the occurrence of a shifting during the installation of a bearing.
2. Description of the Related Art
Referring to FIG. 8 for a general tool used for installing or removing an axle device, the tool is a traditional bearing installing device, and the installing device 9 includes a screw rod 91, a driving portion 911 disposed at an end of the screw rod 91 for rotating the screw rod 91, a driving unit 93 screwed around the external periphery of the screw rod 91 for rotating the screw rod 91 and pushing a connecting base 92, and a plurality of push rods 94 connected to the connecting base 92. The screw rod 91 has a spring 95 disposed on the external periphery of the screw rod 91 and at an end away from the driving portion 911 for resuming the connecting base 92 into its original position, and the screw rod 91 has an axial connection unit 96 disposed at an end away from the driving unit 93 for connecting the screw rod 91 with an axle device 97.
During use, the screw rod 91 is fixed to the axle device 97 by the axial connection unit 96, and then the driving unit 93 is rotated to push the connecting base 92 to move in a direction towards the axle device 97, and drive each push rod 94 to move, so that each push rod 94 props and pushes a desired installing bearing 98 to embed and engage the bearing 98 onto the axle device 97.
However, this kind of manual driving device requires a driving unit 93 with a longer arm of force, but if the manual driving device is used in a narrow space, then the radius of gyration of the arm of force of the driving unit 93 will be too large, and thus causing the manual driving device unable to use. 
Referring to FIGS. 9 and 10 for another improved installing device, the installing device 8 includes a screw rod unit 81 driven by a hydraulic pump, and an extension rod 811 disposed in the screw rod unit 81 and extended when the hydraulic pump is driven. The screw rod unit 81 includes a containing cylinder 82 screwed onto an end away from the hydraulic pump and having a plurality of equidistant slide grooves 821. The bottom of the containing cylinder 82 has a screw hole 822 for screwing a latch element 841 that is coupled to a coupling element 83, and the coupling element 83 is secured onto a spindle of an axle device 85.
The containing cylinder 82 includes a slide base 86 disposed therein, and the slide base 86 includes a containing cavity 861 disposed at an end of the extension rod 811 for containing the screw rod unit 81. The slide base 86 has a plurality of equidistant protruded wings 862 respectively corresponding to each slide groove 821 of the containing cylinder 82, and each protruded wing 862 is passed with a push rod 87, and a spring is installed between the slide base 86 and the bottom of the containing cylinder 82 for resuming the slide base 86 into its position, and each push rod 87 is screwed with an extension rod 871 to increase the length, and the containing cylinder 82 has a stop ring 89 screwed at an end away from the bottom.
During use as shown in FIG. 10, the coupling element 83 is secured onto a spindle of the axle device 85, and the containing cylinder 82 is latched with the coupling element 83 by a latch element 84 that is coupled with the bottom. After each push rod 87 is pushed towards the external periphery of the axle device 85, and the hydraulic pump is pressed to push the extension rod 811 in the screw rod 81, the slide base 86 is moved downward to further push a bearing 851 to be embedded and engaged with the axle device 85 for the installation.
The method of installing a bearing by a single spring to press the slide base is adopted in the installation process. Since only one spring is installed at the position of the spindle of the containing cylinder, each push rod of the slide base may be shifted due to the biased bearing occurred when the bearing is pressed. As a result, each push rod becomes less stable when the bearing is installed and pressed, and the  common center of the bearing and the axle device may be deviated easily, and thus it is necessary to remove the bearing from the axle device by a tool and reinstall the bearing. However, the bearing may be damaged and the external periphery of a component such as the axle device may be worn out easily in the process.